Initial ranging means a procedure of controlling transmission parameters (frequency offset, time offset, transmission power) for uplink communication between a mobile station and a base station during an initial network registration. After performing the network registration procedure, the mobile station performs periodic ranging to continue to maintain uplink communication with the base station. In addition, an example of ranging includes handover ranging for simplifying a procedure during a handover operation of a mobile station.
In a broadband wireless access system, a CDMA code (or ranging preamble) set that can be used for ranging depending on ranging types and a region for transmitting CDMA codes are allocated through a channel (for example, UL-MAP in case of 802.16e system and SFH in case of 802.16m system), which broadcasts system information, by a network. Accordingly, in order to perform handover ranging, a specific mobile station selects a specific code from CDMA codes for handover ranging and transmits the selected code to the base station through initial ranging and handover ranging regions, i.e., ranging opportunity, thereby requesting ranging. In this case, the network may identity a type of ranging through the received CDMA code and a region to which the CDMA code is transmitted.
A ranging acknowledgement response (AAI_RNG-ACK) message and a CDMA allocation map information element (CDMA Allocation A-MAP IE) are used for the ranging procedure, wherein the ranging acknowledgement response message is to notify the mobile station whether the base station has received the ranging code received during the ranging procedure, and the CDMA allocation map information element is to transfer resource allocation information for the successfully received ranging code to the mobile station that has transmitted the corresponding code.
Hereinafter, an idle mode of a mobile station and a paging group related to the embodiments of the present invention will be described in brief.
The idle mode generally refers to an operation for enabling downlink (DL) broadcast traffic reception to be periodically performed although a mobile station is not registered in a specific base station, when the mobile station is moved in a radio link environment including multiple base stations.
If the mobile station does not receive traffic from the base station for a predetermined time, the mobile station may be shifted to the idle mode for power saving. The mobile station which has shifted to the idle mode may receive a broadcast message (for example, a paging message) transmitted by the base station for an available interval and determine whether the mobile station shifts to a normal mode or is in the idle mode. In addition, the mobile station which is in the idle mode performs location update so as to inform a paging controller of its location.
The idle mode may eliminate demands for activation associated with handover and demands for a general operation so as to provide benefits to the mobile station. The idle mode may restrict the activity of the mobile station to be scanned in a discrete period so as to reduce power consumption and operational resources used by the mobile station.
In addition, the idle mode may provide a simple appropriate scheme for informing a mobile station of pending downlink traffic, and eliminate radio interface and network handover (HO) traffic from an inactive mobile station so as to provide benefits to a network and a base station.
Paging refers to a function for recognizing the location (for example, any base station or any mobile switching center) of a Mobile Station (MS) when an incoming signal occurs in mobile communication. A plurality of Base Stations (BSs) for supporting the idle mode may be included in a specific paging group so as to configure a paging area.
The paging group may include at least one base station BS. One base station may be included in one or more paging groups. A paging controller may manage a list of mobile stations, which are in the idle mode, using a paging-announce message which is one of backbone network messages, and manage initial paging of all the base stations BSs belonging to the paging group.
In order to increase a hit ratio of paging, the mobile station may perform a location update procedure. Location update. In this case, the location update is an operation of the mobile station to increase the hit ratio of the paging to the mobile station having entered the idle mode and indicates a process for a mobile station to report a new location or region, which is entered by the mobile station when the mobile station moves into a new region, to a network. Such a location update procedure may be performed through the aforementioned ranging procedure. In other words, the location update procedure may be performed in a manner that ranging preamble and ranging MAC message (that is, a ranging request (RNG-REQ) message and a ranging response (RNG-RSP) message) are exchanged between the mobile station and the base station.
Hereinafter, an example of a procedure of enabling a mobile station to enter an idle mode in a general IEEE 802.16 system will be described with reference to FIG. 1.
Referring to FIG. 1, the mobile station transmits a deregistration request (DREG-REQ) message to a serving base station to switch a normal mode to the idle mode (S101).
The serving base station which has received the deregistration request (DREG-REQ) message may transmit or receive mobile station information and serving base station information to or from a paging controller. In other words, the serving base station may inform the paging controller of an ID of a mobile station which enters the idle mode and an ID of the serving base station. In addition, the paging controller may inform the serving base station of a paging group ID (PG ID) or a paging controller ID (PC ID). The paging group ID or the paging controller ID may be used to transmit or receive a paging message (S102).
Next, the serving base station may transmit a deregistration command (DREG-CMD) message to the mobile station in response to the deregistration request message. The deregistration command message may include paging information. At this time, the paging information may include a paging cycle parameter, a paging offset parameter and a paging listen interval parameter. In addition, the deregistration command message may further include a paging controller ID and a Paging Group (PG) ID (S103).
The mobile station which has received DREG-CMD message may enter the idle mode by confirming that an idle mode entry request has been successfully accepted. The mobile station may receive the paging message on the basis of the paging information received through the DREG-CMD message. That is, the mobile station may monitor a radio channel so as to determine whether a paging message is transmitted thereto during the paging listen interval. During the remaining interval of the paging cycle, the mobile station operates in a sleep mode or a radio turn-off mode so as to reduce power consumption (S104).
A call or an external packet may be input to the paging controller (S105).
Accordingly, the paging controller may perform a paging procedure for paging the mobile station. At this time, the paging controller may transfer a paging announcement message to all the base stations within the paging group (S106).
All the base stations in the paging group, which have received the paging message, may broadcast an MOB_PAG-ADV message to all the mobile stations managed by them (S107).
The mobile station confirms the MOB_PAG-ADV message, and enters the normal mode and performs communication with the serving base station when the paging controller performs paging with respect to the mobile station (S108 and S109).
However, in the IEEE 802.16m system, the mobile station and the base station exchange a short message service (SMS) by using a second layer transmission (AAI_L2-XFER) message. The mobile station which has entered the aforementioned idle mode may transmit the SMS to the base station through the ranging request message during a location update procedure or a network reentry procedure or receive the SMS from the base station through the ranging response message. However, a procedure of enabling a transmitter to efficiently know whether a receiver has successfully received SMS transmitted through ranging request/response messages has not been defined.